The present invention relates to an automatic dispensing machine for automatically dispensing accurately a predetermined quantity of liquids required to be stored at a constant temperature. The present invention is also applicable to an automatic inspection machine utilizing reagents, etc. and an automatic incubator in which culture solutions, etc. are dispensed.
Conventionally, in dispensing machines, it has been so arranged as shown in FIG. 1 that liquid in a liquid tank 2 enclosed by a constant temperature bath 1 is directly dispensed into a container 4 by using a discharge pump 3. A dispensing quantity of the liquid set at this time is controlled on the basis of an operating time of the discharge pump 3. Meanwhile, a tube 5 extending from the liquid tank 2 to the container 4 through the discharge pump 3 is empty at the time of start of dispensing of the liquid. Therefore, in order to fill the tube 5 with the liquid prior to start of dispensing of the liquid of the liquid tank 2, a discharge opening 6 is required to be displaced to a waste liquid container 8 by a displacement mechanism 7 such that the liquid is discharged from the discharge opening 6 into the waste liquid container 8.
In the known dispensing machines, the liquid of the liquid tank 2 is directly dispensed into the container 4 by the discharge pump 3 and the dispensing quantity of the liquid is controlled based on the operating time of the discharge pump 3. Thus, the known dispensing machines have such drawbacks that the dispensing quantity of the liquid changes due to deterioration of the tube 5 or according to presence or absence of droplets at the discharge opening 6 and that the tube 5 is fractured due to defective setting of the tube 5, thereby resulting in excessive reduction of the dispensing quantity of the liquid.
Furthermore, in the known dispensing machines, since the tube 5 is empty at the time of start of dispensing of the liquid, the tube 5 is required to be filled with the liquid initially. In the known automatic dispensing machines in which the liquid is drawn into the waste liquid container 8 before the liquid is dispensed into the container 4, an operator cannot judge whether the tube 5 has been filled with the liquid. Therefore, the known automatic dispensing machines have such a disadvantage that dispensing of the liquid into the container 4 should be started after the liquid has been sufficiently delivered into the waste liquid tank 8, thus resulting in increase of waste of the liquid.
Meanwhile, in response to recent progress in study of biotechnology, automatic culture processing apparatuses for efficiently culturing microorganisms have been developed greatly. In culture of microorganisms, either cells to be cultured or bacteria to be cultured and culture solution are usually introduced into a number of wells arranged in a pattern of a matrix on a tray and then, the wells are covered by a lid such that proliferation of the cells or the bacteria is effected in a temperature controlled room for a certain time period. During proliferation of the microorganisms, replenishment, exchange or change of the culture solution is necessary. To this end, in the prior art automatic culture processing apparatuses, a plurality of pipets are moved upwardly and downwardly by a lifting mechanism and tips of the pipets are inserted into the wells such that exchange of the culture solution, i.e. suction and discharge of the culture solution are performed. For example, wells arranged in a pattern of an 8.times.12 matrix, namely 8 (number of rows of the matrix) wells in a sldewise direction of the tray and 12 (number of columns of the matrix) wells arranged in a longitudinal direction of the tray are provided on a tray in common use. In this case, 8 pipets corresponding to the 8 wells in the sidewise direction of the tray are provided so as to be moved horizontally in one direction by a drive mechanism such that replenishment, exchange or change of the culture solution is performed at all the wells.
However, the above described exchange, etc. of the culture solution is not always performed at all the wells. Namely, in the case where germs have been mixed into a specific one of the wells in the course of culture of the microorganisms, germicide is syringed into the specific well and the culture solution is not required to be discharged into the specific well by inserting thereinto the pipet in the subsequent exchange, etc. of the culture solution. 0n the contrary, it is necessary to prevent the germicide from attaching to the pipet through insertion of the pipet into the specific well.
However, the prior art automatic culture processing apparatuses provided with a plurality of the pipets has been disadvantageous in that since exchange, etc. of the culture solution is performed at the wells of one row or one column of the matrix simultaneously, the pipets cannot be used if there exists a well having germs mixed thereinto.
Furthermore, in the prior art automatic culture processing apparatuses, exchange, etc. of the culture solution are performed by inserting the tips of the pipets into the wells, the tips are brought into contact with the culture solution in the wells, so that such a problem arises that if the identical pipets are used, transfer of germs, etc. among the wells or between the trays occurs. Therefore, in order to obviate such a problem, a detachable tip is provided at a distal end of each of the pipets such that contamination of the culture solution by the germs is prevented through exchange of the tips. Since a long time period is required for exchange of the tips and the distal end of each of the pipets may be bent if the tips are exchanged manually, it is desirable to automate exchange of the tips. For example, in the case of the wells arranged in a pattern of a 8.times.12 matrix, not only the tray or the pipets should be moved horizontally but the pipets should be moved vertically in order to gain access to the wells. Thus, generally, when automatic culture processing apparatuses are of a type in which the pipets are moved horizontally, it is desirable that a movable portion is reduced in weight so as to decrease power consumption for driving the movable portion and a tip exchange mechanism is both light in weight and simple in construction at the movable side. However, such automatic culture processing apparatuses are not known at present.